Electrochemical energy storage systems, such as batteries, supercapacitors and the like, have been widely proposed for large-scale energy storage applications. Various battery designs, including flow batteries, have been considered for this purpose. Compared to other types of electrochemical energy storage systems, flow batteries can be advantageous, particularly for large-scale applications, due to their ability to decouple the parameters of power density and energy density from one another.
Flow batteries generally include negative and positive active materials in corresponding electrolyte solutions, which are flowed separately across opposing faces of a membrane or separator in an electrochemical cell containing negative and positive electrodes. The terms “membrane” and “separator” are used synonymously herein. The flow battery is charged or discharged through electrochemical reactions of the active materials that occur inside the two half-cells. As used herein, the terms “active material,” “electroactive material,” “redox-active material” or variants thereof synonymously refer to materials that undergo a change in oxidation state during operation of a flow battery or like electrochemical energy storage system (i.e., during charging or discharging). Although flow batteries hold significant promise for large-scale energy storage applications, they have often been plagued by sub-optimal energy storage performance (e.g., round trip energy efficiency) and limited cycle life, among other factors. Despite significant investigational efforts, no commercially viable flow battery technologies have yet been developed.
The operating performance of flow batteries can be impacted by a number of factors including, for example, state of charge (SOC), operating temperature, age of the flow battery and its components, electrolyte circulation rates, power and current conditions, and the like. As used herein, the term “state of charge” (SOC) refers to the relative amounts of reduced and oxidized active material species at an electrode within a given half-cell of a flow battery or other electrochemical system at a particular operation time. In many cases, the foregoing factors are not independent of one another, which can make performance optimization very difficult. Effective regulation of circulation rates throughout a flow battery is one particular factor that has been especially problematic to address and has contributed to their present lack of commercial viability.
In view of the foregoing, flow batteries and associated methods configured to promote more effective circulation of an electrolyte solution would be highly desirable in the art. The present disclosure satisfies the foregoing needs and provides related advantages as well.